How to make particles fall and land into predetermined shapes (like text)?
You could do it backwards.  Have a mesh (set to not be visible in the render itself) define the shape for the particles to end up in, have this mesh start with a lot of particles only inside its volume, and then animate them all 'falling' randomly upwards under an appropriate force.  Then reverse the animation, either externally or via baking it and reversing the order of keyframes.
Whether this looks good or very faked will depend on the look you're going for and the shapes of your targets.